Ultraviolet and infrared focal place array

ABSTRACT

The two-color focal plane array detects a target or image a target in the traviolet (UV) and infrared (IR) simultaneously. The system is a correlation, contrast or moving target tracker with very good countermeasure capability against a ground, sea, or airborne target. The tracker/seeker can be an all solid state no-moving parts configuration with the two focal plane devices of detectors aligned in their layer so as to be at an effectively cofocal.

DEDICATORY CLAUSE

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto me of any royalties thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the present invention.

FIG. 2 is a top view showing the arrangement of the detectors.

FIG. 3 is a side view of the array without thin films showing thepresent invention.

FIG. 4 shows a simplified engagement diagram for the focal plane arraytracker system.

FIG. 5 is an illustration of a particular example of the use of thedevice.

FIGS. 6A and 6B are diagrams illustrating the output amplitudes of thedetectors in relationship to the specific illustration of FIG. 5.

DESCRIPTION OF THE BEST MODE AND PREFERRED EMBODIMENT

FIGS. 1-3 show a two-dimensional UV/IR (ultraviolet infrared) focalplane array which will be used to look out into space in two-dimension(azimuth and elevation). The sensor consists of cadimium sulfide (CdS)Schottky diode photovoltaic ultraviolet (UV) detectors 12 and a likenumber of infrared (IR) photoconductive or photovoltaic detectors 18.The UV detectors 12 are located in the front of the array and the IRdetectors 18 are in the rear of the array. The distance between thefront and back detectors are optically close, so that the two detectorsare cofocal.

In order to increase the strength and rigidity of the arrays an IRtransparent substrate 19 such as sapphire can be used (see FIG. 1). Toincrease the UV detector efficiency a thin film reflector 14 can beadded between substrate 13 and 15 and a thin film anti-reflectioncoating 11 can be added on the front face of the UV detectors 12. Inorder to discriminate and limit the detected UV wavelengths, a UV thinfilm bandpass filter 10 can be added on the anti-reflection coatings 11of the UV detectors. This UV bandpass filter could be located in thefront optics if desired, and the thin bandpass would not be needed. TheIR detected wavelengths can be limited and discriminated by adding an IRthin film bandpass filter 16 between substrates 15 and 19.Anti-reflection thin film coatings 17 can be added to the front faces ofthe IR Detectors 18 if necessary. The shape of the array can be circularor square or any other required shape.

FIG. 3 shows the basic device without the thin films. Although thedetector elements 12 and 18 are aligned (they could be shifted slightlywith respect to each other without substantial loss of circular logic),the signal input is of a size whereby more than enough IR radiationpasses through detector 12 to activate detector 18. Substrates 13 and 19can be made of any conventional charge-coupled device material such asgallium arsenide. Detector 12 is highly transparent to IR radiation.

FIG. 2 shows a top view of a 11 by 11 two dimensional array which couldbe used for detector 12 or 18. Row 6, column 6 is identified . Othershapes can be used.

FIG. 4 shows the three main parts of the tracker/seeker focal planearray configuration. The target 41 can be airborne or on the ground;moving or not moving. The front end optics 42 gathers the optical IR/UVenergy and projects the energy on the focal plane array 43 at a pitchand yaw angle relative to the axis of the optics or body of thetracker/seeker. The optics can be any of the well known focusing devicesand can be mirrors or lens or a combination of mirrors and lens. Theshape of the array 43 and the number of detectors will depend on thespecific application. The signal processor 44 can be bipolar, MOSFET,Junction FET, charge-coupled devices or charge injection devices and theoutput can be displayed or be the main parameter in a missile guidancecontrol circuit.

One Complete Operation Cycle

A target has a UV background radiation wavelength of x micro-meters andemits an IR radiation wavelength of say 10x micro-meters. This UV/IRenergy is gathered by the front optics 42 and is projected on the focalplane array as shown in FIG. 4. Assume the target 41 is at a longdistance so that the target can be treated as a point source as shown inFIG. 5, and let the optics be aligned at the target so that the UV/IRradiation energy is focused on row 6, column 6 detector as shown inFIGS. 2 and 5. For an airborne target the preferred operation is asfollows. Assuming a point source the UV/IR energy will be detected bydetectors 12 and 18 in row 6 column 6 as shown in FIG. 5. Thewavelengths of the detected energy will be determined by the respectivebandpass filters as shown in FIG. 1. The CdS UV detector 12 is locatedin the front of the array because it is highly transparent to IRradiation and detects or absorbs most of the UV radiation.

For an airborne target with UV background radiation present, thepreferred detection operation is shown in FIGS. 5 and 6. The target 41will block or greatly reduce the detected UV radiation; however, thedetected IR radiation (FIG. 6B) will be much greater than the backgroundIR radiation (FIG. 6A). The signal processor 44 processes these signalsand determines that it is a true target when a given section of eachdetector (such as row 6, column 4) shows a relative low UV value and arelating high IR value. If the target attempt to jam the IR detector byemitting flares or other common methods, the signal processor willignore these signals, because a true target is determined by thecombination of a small UV detector output and a large IR detectoroutput. Effective jamming of the UV detector with ths combination ofradiations is not probable.

As the target comes closer to the tracker more detector elements will beinvolved in the detection and signal processing operation. Severaldetectors adjacent to row 6 column 6 detector could be involved in thedetection process. In this case the signal processor will track thetarget using the centroid of the IR and UV detectors, and if asufficient number of detectors are involved, an image can be developedand displayed. Other signal processing techniques are possible. Any ofthe well known signal processors can be used with proper programmingdesign.

The system can be an anti-missile weapon system where the missile isguided inertially to a point in space, and then the seeker guides themissile onto the target. The inertial and seeker system could be allsolid-state construction and could withstand a high-g environment. Ashorter range application, using the same engagement technique, is aChaparral type weapon system. If a connection with the missile is madeso that the output of the Focal Plane Array (FPA) is displayed on thegunners Forward Looking Infrared (FLIR), along with the targets, then itwould be possible to select a target for each missile and fire allmissiles at the same time or rapid fire all missiles for close-intargets. For longer range targets, using the FLIR to select targets andknowing the range, the missile inertial system could be used to placethe missiles in a target intercept path and then let the seeker guide tothe target after the seeker acquires the target. All the missiles couldbe launched at the time or rapid fired if desired.

In a manportable short range application such as the STINGER-POST weaponsystem the inertial part of the system would not be needed. If aconnection is made with the missile and the output of the FPA isdisplayed on a gunners video screen, then a target in the IR or UV orboth could be selected. In this case a considerable cost savings wouldresult because a night sight would not be needed.

I claim:
 1. In a device comprising a plurality of first detectorsarranged in a plane so as to constitute a first layer; said firstdetectors detecting a first band of radiation; a plurality of seconddetectors arranged in a plane so as to constitute a second layer; saidsecond detectors detecting a second band of radiation; said first andsecond layers being arranged one on top of the other; said device sensesradiation which flows through said first layer into said second layer;said plurality of first detectors being substantially transparent tosaid second band of radiation; said plurality of first and seconddetectors each constitute an array of detectors in its layer; a frontend optics for focusing incoming radiation onto said first and secondlayers; said first band of radiation is ultraviolet; said second band ofradiation is infrared; said plurality of first detectors are cadmiumsulfide ultraviolet detectors arranged in a thin film substrate; andsaid plurality of second detectors are infrared detectors arranged in athin film substrate.